Rumsfeld is scheduled to attend a security conference in Singapore June 4-5 that is expected to draw defense ministers and other policymakers from around the region, and then travel to Bangkok for meetings with Thai officials, they said.

The trip is only the third to east Asia by Rumsfeld, whose time in office has been dominated by conflicts in Afghanistan and Iraq despite a long-running diplomatic standoff with North Korea over its nuclear weapons program.

North Korea and China's military buildup are expected to be at the top of Rumsfeld's agenda both in bilateral meetings with regional defense ministers and in a speech Saturday to the conference, which is organized by the International Institute of Strategic Studies, US defense officials said.

The trip comes amid North Korea's refusal to reactivate six-party talks on its nuclear programs and worries that Pyongyang may take another dramatic step by testing a nuclear weapon.

A senior US defense official, who briefed reporters on Rumsfeld's trip last week, said there was no new information suggesting North Korea was about to test, but he expressed concern that it is on an unpredictable "escalatory ladder."

"We can't predict what the events on that ladder will be," he said. "But we're always concerned when they say things, because sometimes, or a lot of times, when they say they are going to do things, they actually do do them."

While North Korea will be heavily featured in Rumsfeld's talks in Singapore, the secretary is unlikely to use the conference to discuss possible common responses that might be taken if Pyongyang tests a weapon, the official said.

The conference may offer a glimpse at where US-Chinese relations are headed.

While looking to Beijing for help in reining in North Korea, the United States also is worried about a Chinese military buildup that some US analysts believe is tipping the balance against Taiwan, raising the risk of conflict.

An annual Defense Department report on Chinese military power that is due out soon is expected to detail advances China has made in modernizing its forces.

Rumsfeld, who met in April with Chinese military leaders, has said the United States hopes China will play a constructive role in regional security but is uncertain what path it will take.

China has been irritated by US-Japanese efforts to update their alliance and strengthen defense ties, recently declaring Taiwan a common security concern.

A senior Chinese official was expected to make a speech to the conference on China's new role in east Asia.

From southeast Asia, Rumsfeld will fly to Norway next week for talks with officials ahead of a NATO defense ministers meeting in Brussels.